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1.9.1 Biogeochemical Pathways
A biogeochemical cycle is a pathway in which chemical transport occurs through
abiotic and biotic components of the earth.
The most well-known biogeochemical cycles are as follows:
• Carbon cycle.
• Nitrogen cycle.
• Oxygen cycle.
• Phosphorus cycle.
• Sulfur cycle.
• Water cycle.
The newly studied biogeochemical cycles include the following:
• Atrazine cycle.
• Mercury cycle.
Concentrations of the atmospheric carbon dioxide (CO 2 ), methane (CH 4 ), and
nitrous oxide (N 2 O) in 2011 surpassed the concentrations recorded in ice cores for
the period of the past 800 kyr (Stocker et al. 2013).
1.9.1.1 Water Cycle
Water cycle (Fig. 1.21) is one of the important biogeochemical cycles. The sun heats
the water in the oceans and on surface of the earth. Some of it evaporates and some
parts of water will enter the atmosphere by transpiration (loss of water from aerial
parts of the plants). Some parts of water trapped in snow and ice will sublimate
directly into vapor. Evaporation and transpiration together are termed as evapotranspiration. The water vapor rises in the atmosphere and condenses to form clouds and
falls as precipitation. Some precipitation falls as rain, hail, and snow. Snow in
warmer climates melts and joins surface water bodies. Some water bodies are
formed due to melting of hail and collection of surface water. Surface water trickles
into the ground. Some groundwater emerges whereas some groundwater discharge
into surface water.
Some water will be trapped in living things, which will be released to the environment during death, decay, drying, excretion, and transpiration. Some of the water
molecules may react with other chemicals and become a new chemical.
1.9.1.2 Carbon Cycle
The carbon cycle (Fig. 1.22) is one more important biogeochemical cycle.
Following are the major reservoirs of carbon:
• Atmosphere.
1.9 Biochemistry
1.9.1 Biogeochemical Pathways
A biogeochemical cycle is a pathway in which chemical transport occurs through
abiotic and biotic components of the earth.
The most well-known biogeochemical cycles are as follows:
• Carbon cycle.
• Nitrogen cycle.
• Oxygen cycle.
• Phosphorus cycle.
• Sulfur cycle.
• Water cycle.
The newly studied biogeochemical cycles include the following:
• Atrazine cycle.
• Mercury cycle.
Concentrations of the atmospheric carbon dioxide (CO 2 ), methane (CH 4 ), and
nitrous oxide (N 2 O) in 2011 surpassed the concentrations recorded in ice cores for
the period of the past 800 kyr (Stocker et al. 2013).
1.9.1.1 Water Cycle
Water cycle (Fig. 1.21) is one of the important biogeochemical cycles. The sun heats
the water in the oceans and on surface of the earth. Some of it evaporates and some
parts of water will enter the atmosphere by transpiration (loss of water from aerial
parts of the plants). Some parts of water trapped in snow and ice will sublimate
directly into vapor. Evaporation and transpiration together are termed as evapotranspiration. The water vapor rises in the atmosphere and condenses to form clouds and
falls as precipitation. Some precipitation falls as rain, hail, and snow. Snow in
warmer climates melts and joins surface water bodies. Some water bodies are
formed due to melting of hail and collection of surface water. Surface water trickles
into the ground. Some groundwater emerges whereas some groundwater discharge
into surface water.
Some water will be trapped in living things, which will be released to the environment during death, decay, drying, excretion, and transpiration. Some of the water
molecules may react with other chemicals and become a new chemical.
1.9.1.2 Carbon Cycle
The carbon cycle (Fig. 1.22) is one more important biogeochemical cycle.
Following are the major reservoirs of carbon:
• Atmosphere.
1.9 Biochemistry